Polyatomic Lewis structure

In the Lewis structure of a molecule or polyatomic ion, valence electrons ordinarily occur in pairs. There are two kinds of electron pairs. 

Draw Lewis structures for molecules and polyatomic ions. 

Write the Lewis structures for the following molecules and polyatomic ions. In each case, the first atom is the central atom. 

Give the formula of a polyatomic ion that you would expect to have the same Lewis structure as... 

Each atom in a polyatomic molecule completes its octet (or duplet for hydrogen) by sharing pairs of electrons with its immediate neighbors. Each shared pair counts as one covalent bond and is represented by a line between the two atoms. A Lewis structure does not portray the shape of a polyatomic molecule it simply displays which atoms are bonded together and which atoms have lone pairs. 

HOWTO WRITE THE LEWIS STRUCTURE OF A POLYATOMIC SPECIES... 

The Lewis structure of a polyatomic species is obtained by using all the valence electrons to complete the octets (or duplets) of the atoms present by forming single or multiple bonds and leaving some electrons as lone pairs. 

One form of the polyatomic ion I, has an unusual V-shaped structure one I atom lies at the point of the V, with a linear chain of two I atoms extending on each side. The bond angles are 88° at the central atom and 180° at the two atoms in the side chains. Draw a Lewis structure for L that explains its shape and indicate the hybridization you would assign to each nonterminal atom. 

C09-0069. Determine the Lewis structure of each of the following polyatomic ions. Include all resonance structures and formal charges, where appropriate (a) NO3 (b) HSO4 (c) C03 and (d)... 

C09-0070. Determine the Lewis structure of each of the following polyatomic ions. Include all resonance... 

C09-0107. Write Lewis structures and calculate formal charges for the following polyatomic ions (a) bromate (b) nitrite (c) phosphate and (d) hydrogen carbonate. 

Trigonal-bipyramidal species and nucleophilic displacement reactivity The 3c/4e cu-bonding motif can also be achieved in nonlinear polyatomics by backside attack of a nucleophile X - on a polar Y—Z bond of a conventional Lewis-structure molecule,... 

It is also possible to write a Lewis structure for polyatomic anions or cations. The N - A = S rule can be used, but for an anion extra electrons equal to the magnitude of the negative charge must be added to the electrons available. If the ion is a cation, you will need to subtract number of electrons equal to the charge. 

Sometimes when writing the Lewis structure of a species, we may draw more than one possible correct Lewis structure for a molecule. The nitrate ion, N03 , is a good example. The structures that we write for this polyatomic anion differ in which oxygen has a double bond to the nitrogen. None of these three truly represents the actual structure of the nitrate ion—it is an average of all three of these Lewis structures. We use resonance theory to describe this situation. Resonance occurs when more than one Lewis structure (without moving atoms) is possible for a molecule. The individual structures are called resonance structures (or forms) and are written with a two-headed arrow (<- ) between them. The three resonance forms of the nitrate ion are ... 

When writing the Lewis structures of polyatomic ions, don t forget to show their ionic charge. 

When using the N - A = S rule in writing Lewis structures, be sure you add electrons to the A term for a polyatomic anion, and subtract electrons for a polyatomic cation. 

You can use the procedure outlined below to draw the Lewis structures for molecules and ions that have a central atom, with other atoms around it. The Sample Problems and additional text that follow show how to apply these steps for several molecules and polyatomic ions that obey the octet rule. Afterwards, use Practice Problems 9 to 13 to practice drawing Lewis structures. 

Keep in mind that the need for an expanded valence level for the central atom may not always be as obvious as in the previous Sample Problem. For example, what if you were asked to predict the molecular shape of the polyatomic ion, BrCU" Drawing the Lewis structure enables you to determine that the central atom has an expanded valence level. 

You have seen examples of how Lewis structures can be used to assign oxidation numbers for polar molecules such as water, non-polar molecules such as chlorine, and polar polyatomic ions such as the cyanide ion. 

Use Lewis structures to assign an oxidation number to each element in the following polyatomic ions. 

Drawing Lewis structures to assign oxidation numbers can be a very time-consuming process for large molecules or large polyatomic ions. Instead, the results from Lewis structures have been summarized to produce a more convenient set of rules, which can be applied more quickly. Table 10.1 summarizes the rules used to assign oxidation numbers. You may have discovered some of these rules for yourself in the ThoughtLab you just completed. 

TOOLBOX 2.1 How to write the Lewis structure of a polyatomic species... 

We begin to write Lewis structures for polyatomic species just as we did for methane ... 

EXAMPLE 2.3 Writing Lewis structures for polyatomic molecules... 

Phosphorus pentachloride is an ionic solid consisting of PC14+ cations and PC16 anions, and it sublimes at 160°C to a gas of PCI, molecules. The Lewis structures of the polyatomic ions and the molecule are shown in (33). Although the cation is a polyatomic ion in which the P atom does not need to expand its valence shell, in the anion the P atom has expanded its valence shell to 12 electrons, by making use of two of its 3d-orbitals. In PC15, the P atom has expanded its valence shell to 10 electrons by using one 3d-orbital. 

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